G. Den Boef

Determination of total ammoniacal introgen in water by flow injection analysis and a gas diffusion membrane

A simple flow injection method for the spectrophotometric determination of ammonia and ammonium ions is described. Ammonia diffuses through a gas-permeable membrane, causing an absorbance change of an acid-base indicator solution (bromothymol blue). The detection limit is about 10−6 mol l−1, the response is linear in the concentration range 10−6-10−4 mol l−1, the sample rate is 100 h−1, and the standard deviation at 10−5 mol l−1 is about 3%.

The formation of mixed copper(II) sulfide—silver(I) sulfide membranes for copper(II)-selective electrodes

Abstract Several methods for the preparation of mixed copper(II) sulfide—silver(I) sulfide precipitates have been investigated. Pellets of these materials have been tested for their suitability as copper(II)-selective membranes. Homogeneous membranes with satisfactory electrochemical properties can be prepared only from precipitates obtained by addition of the metal salts to sodium sulfide Membrane leakages, limits of detection, calibration curves and titration curves with different types of precipitate are discussed.

The formation and properties of mixed lead sulfide—silver sulfide membranes for lead(II)-selective electrodes

Abstract The preparation and behaviour of a lead(II)-selective electrode made of mixed silver sulfide-lead sulfide are discussed and compared with those of a copper(II)-selective electrode. X-ray diffraction showed that hot-pressing of the membrane causes changes in the crystalline structure of the material. Responses to lead(II), sulfide, and hydroxide were measured ; potential-pH curves were determined in solutions containing EDTA, NTA, Tetren or Trien with and without the lead complex. The results are similar to those obtained for the copper-i.s.e. Data are given for titrations, selectivity coefficients, and response times. The response of the lead-i.s.e. to an addition of ligand is faster for Trien than for EDTA. This difference is large for the copper-i.s.e. These response rates may be correlated with potential-pH curves in the presence of ligands.

Spectrophotometric determination of chromium(iii) with complexans

Abstract Selective spectrophotometric determinations of milligrain amounts of chromium(III) with complexans are described, based on the fact that the chromium(IIl) complexes are formed rapidly at boiling temperatures, but very slowly at room temperature, while the formation of some interfering complexes takes place instantaneously. Determinations with EDTA are more sensitive, but the combined presence of cobalt and other metals still interferes; there is no interference with the less sensitive NTA. The combined presence of a l00-fold amount of copper, nickel, cobalt and iron generally has no effect on the results. The use of DCTA, DTPA and HEDTA is discussed.

The application of strongly reducing agents in flow injection analysis: Part 1. Chromium(II) and vanadium(II)

Abstract Many reagenst cannot easily be applied in quantitative analysis, because of their instability under atmospheric conditions. When such reagents are prepared in a flowing stream, their applicability is very promising; for example, in flow injection analysis, a reagent need be stable only for 20–30 s. The application of chromium(II) and vanadium(II) in flow injection analysis is described. Nitrate and nitrile can be determined in the concentration range 5 × 10 −5 −5 × 10 −3 . Calibration graphs show good linearity.

Solid-state ion-selective electrodes as end-point detectors in ompleximetric titrations: Part I. The titration of mixtures of two metals

Abstract The compleximetric titration of mixtures of copper(II) and other metal ions by means of potentiometric indication with a copper(II)-selectivc electrode has been investigated. The theoretical titration curves have been calculated, the effects or the selectivity of the electrode and the limit of detection of the electrode being taken into account. The experimental curves generally agree very well with the theoretical curves. Determinations in the range 10-3–10-5M are possible

The application of strongly reducing agents in flow injection analysis: Part 4. Uranium(III)

Abstract The application of vanadium(II) as a powerful reducing reagent in flow injection analysis is described. Results are presented for the determination of various organic and inorganic substances. With spectrophotometric detection, based on the absorption by vanadium(II)-EDTA at 350 nm, limits of determination were about 5 X 10−5 mol 1−1. Nitrate, nitrite and hydroxylamine were measured with amperometric detection. The limit of determination was about the same as with spectrophotometric detection. In a slightly acidic medium, hydrazine could be determined with the amperometric detector, with a limit of determination of about 10−4 mol l−1. By coupling an ammonia detection device to the reduction system, the percentage conversions of nitrate, nitrite and hydroxylamine to ammonia were shown to be 26%, 54% and 47%, respectively.

The application of strongly reducing agents in flow injection analysis : part 2. Chromium(II)

The application of chromium(II) as strongly reducing reagent in flow injection analysis is described in detail. Results of the determination of a number of organic and inorganic substances are presented. With spectrophotometric detection, based on the absorption of chromium(III)—EDTA at 500 nm, limits of determination were of the order 10−4 mol l−1. Polarographic detection was studied for nitrate and nitrite, for which the limit of determination was decreased with respect to spectrophotometric detection by factors of about 3 for nitrate and 10 for nitrite.

Flow injection analysis (FIA) — a personal view

Abstract 36 authors from 10 countries express their viewpoints on the merits of flow injection analysis. Alison Macdonald has contributed invaluably to the development of FIA through critical evaluation of work of all the above authors, by editing manuscripts, and by carefully resolving differences between authors and referees. Therefore Analytica Chimica Acta, together with its Editor, may be regarded as the Alma Mater of FIA. It is our intention to honour (and humour). Dr. Macdonald by publishing this nonorchestrated and, by us, unedited patchwork of individual papers which reflect a rich mixture of applications, modifications and interpretations of FIA, together with a variety of personal opinions. We are most grateful to our colleagues for endorsing this unconventional way of celebrating the 25-year anniversary of our Editor (J.R. and E.H.H.).

Titration curves of compleximetric titrations of mixtures of metal ions with one ligand : Part I. Mathematical expressions

Abstract Formulae were calculated for the compleximetric titration of mixtures of two and of three metals with one ligand, giving the relation between a titration parameter f and the concentration of the metals, the ligand or the complexes separately.